We claim the ornamental design for the cork holder, as shown and described.
FIG. 1 is a perspective view of a cork holder embodying the invention;
FIG. 2 is a front view of the cork holder of FIG. 1; and,
FIG. 3 is a bottom view of the cork holder of FIG. 1.
The broken line showing the environment is for illustrative purposes only and forms no part of the claimed design. The top view, the right side view, the left side view, and the rear view, form no part of the claimed design.